Shaula (Lambda Scorpii)
Coordinates, interferometric distance (570 ly), magnitude 1.62, eclipsing pre-main-sequence companion, and observing guide for Shaula.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Combined apparent visual magnitude (V) | 1.62 mag | ± 0.02 mag | Johnson UBV photometry (Beta Cephei + 5.95-day grazing eclipse dips) | definitive | Hipparcos New Reduction Catalog |
| Interferometric orbital distance | 175 pc | ± 20 pc | SUSI optical interferometry & spectroscopic orbit of wide pair Aa–B (Tango et al. 2006) | high-confidence | SIMBAD Astronomical Database (CDS) |
| Inner eclipsing binary period (Aa–Ab) | 5.9525 d | ± 0.0001 d | WIRE space photometry & radial velocity (outer B companion period = 1,082 ± 3 d) | definitive | SIMBAD Astronomical Database (CDS) |
| Primary component mass (Shaula Aa) | 10.4 M☉ | ± 1.3 M☉ | 3D interferometric + spectroscopic triple solution (Ab = 1.8 ± 0.2 M☉, B = 8.1 ± 1.0 M☉) | high-confidence | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Shaula (Lambda Scorpii Triple System) at RA 17h 33m 36.53s, Dec -37° 06′ 13.8″ within Scorpius, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Shaula (Lambda Scorpii, from the Arabic al-Shawlah meaning 'the Raised Tail') is the second-brightest star in Scorpius after Antares, shining at combined visual magnitude 1.62 at the tip of the Scorpion's venomous stinger. Paired just 35 arcminutes (0.58°) east-northeast of 2.69-magnitude Lesath (Upsilon Scorpii), the two hot blue-white stars form the famous 'Cat's Eyes' asterism hanging low in the southern summer Milky Way.
Long-baseline optical interferometry with the Sydney University Stellar Interferometer (SUSI) combined with space-based WIRE photometry proved that Shaula is a compact, coplanar hierarchical triple system of young stars (~10–13 million years old) located ~175 parsecs (570 light-years) away. The innermost pair consists of Shaula Aa—a 10.4-solar-mass B1.5 IV Beta Cephei pulsating subgiant oscillating every 5.13 hours—orbited every 5.9525 days by Shaula Ab, a 1.8-solar-mass star that produces shallow eclipses and strong coronal X-ray emission.
Because the system is only ~10 million years old, the 1.8-solar-mass companion Shaula Ab has not yet finished contracting onto the hydrogen-fusing main sequence, making it a rare eclipsing pre-main-sequence T Tauri star! Orbiting this inner pair every 1,082 days (2.96 years) at an angular separation of 48 milliarcseconds (~5.5 AU) is Shaula B, a massive 8.1-solar-mass B2 V main-sequence star.
Practical Visual Observing Guide
- Look at the curved hook at the southern end of Scorpius's J-shaped tail: Shaula (mag 1.62) and Lesath (mag 2.69) sit just half a degree apart, fitting comfortably side-by-side inside a single low-power telescope eyepiece or binocular field.
- Just 4° northeast of Shaula and Lesath lies Messier 7 (Ptolemy's Cluster), one of the grandest naked-eye open star clusters in the sky.
Catalog Cross-Identifications & Aliases
Common Aliases: λ Scorpii · HD 158926 · HIP 85927 · 35 Scorpii
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 85927 |
| HD | HD 158926 |
| SIMBAD | * lam Sco |
| WIKIDATA | Q13046 |
Related Objects, Comparisons & Guides
Kaus Australis (Epsilon Sagittarii B9.5 Giant)
Coordinates, Hipparcos distance (143 ly), magnitude 1.85, brightest star in Sagittarius, and observing guide for Kaus Australis.
Sagittarius A* (Galactic Center Black Hole)
Coordinates, GRAVITY S2 stellar orbit distance (8,277 pc) & mass (4.297 × 10^6 M☉), EHT 51.8 μas shadow, and Galactic Center guide for Sgr A*.
Spica (Alpha Virginis Ellipsoidal Binary)
Coordinates, Hipparcos distance (250 ly), 4.01-day close B-star binary, precession discovery history, and observing guide for Spica.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Scientific Sources & Dataset Provenance
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg